Plastic tube manufacture



Nov. 4, 1952 w. A. MERCK Er A1.

PLASTIC TUBE MANUFACTURE Filed June 29, 1950 WNMWI K Y www m m56. R NM 0 n .a n MAW. A

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Nlllmhlnvbmul N Patented Nov. 4, 1952 PLASTIC TUBE MAN UFACTURE William A. Merck, Rutherford, and Mark W. Olson, Allendale, N. J., assignors to United States Rubber Company, New York, N. Y., a corporation of New Jersey Application June 29, 1950, Serial No. 171,136

2 Claims. 1

This invention relates to an improved apparatus for the manufacture of plastic tubes, and it particularly relates to the continuous extrusion and cure of the plastic in tubular form by forcing the plastic through a relatively long sleeve having a long rotatable deectablecore therein which is provided with means for imposing back pressure on the plastic within the sleeve.-

In the continuous extrusion and cure of plastic tubes, a relatively long sleeve and core therein is required, in order to permit the plastic to be cured or set while it is confined between the sleeve and the core. The core is supported only at the inlet end of the sleeve, and due to the relatively long suspended length of core, its free deilectable end has sagged away from the center of the sleeve and produced a plastic tube having a bore, or internal cross-sectional dimension which was non-concentric with the walls of the tube, or external cross-sectional dimension thereof. It has been found that thecore may be retained in a centered position in respect t the sleeve by rotating either the outer sleeve or the inner core, and thereby cause the deectable end of the core to float on the plastic in a central position in respect to the walls of the tube being extruded. In either case, it is required that back pressure be applied to the plastic within the tube by constricting the passage between the core and the sleeve near the discharge end thereof. We have found that when the core is rotated and the plastic is rotated with it, improved results are obtained by aiiixing the restricting means, in the form of a snubber, to the end of the core rather than to the end of the sleeve, thereby eliminating excessive twist of the plastic in the sleeve around the axis of the core. In accordance with our invention an improved expansible snubber is attached to the discharge end 'of the rotatable mandrel to eliminate such excessive twist.

The foregoing objects and other advantages of this invention will be further described in reference to the accompanying drawings in which:

Fig. 1 is a cross-sectional view of an extruding apparatus provided with a rotatable mandrel and a stationary outer sleeve, and in which the snubber is attached to the iioating end of the mandrel at the discharge end of the sleeve in accordance with our invention;

Fig. 2 is a cross-sectional view of the tube forming sleeve and core taken on line 2-2 of Fig. 1;

Fig. 3 is an end view 4of the sleeve and core looking in the direction of the arrows 3-3 of Fig. 1;

Figs. 4 and 5 are views of a 4modified form of a core in a sleeve which corresponds tothe view in Figs. 2 and 3, respectively, but showing a square core and snubber; and

Fig. 6 is a longitudinal cross-section on line ,6-6 of Fig. 5.

2 As shown in Fig. l of the drawings, the plastic P is forced by an extruder I0 through a stationary sleeve II, and around a rotatable core I2 within the sleeve II to continuously form and cure or set a plastic tube T, which is being dis-v charged from the sleeve II. The ow of plastic from the sleeve II is restricted by a snubber I3, which is affixed to the core I2 at the discharge end of the sleeve II for producing a back pressure on the plastic P in the sleeve, and thereby cause it to completely ll the sleeve and form a tube free from voids. The outer surface of the plastic P in the sleeve I'I is lubricated by lubricant which is forced through a pipe I4, attached to the head of the extruder I0, and the internal surface of the plastic P is lubricated by lubricant which is forced through a conduit I5 in the extruder screw I6. The conduit I5 is threaded into a central bore in the screw I6, whereby itis rotated with the screw. The outer end of the conduit I5 extends through the screw I6, and is pro-` vided With a conventional rotary connection (not shown), through which lubricant is supplied v-to the conduit I5.

The extruder screw I6 is rotated by a conventional drive and forces the plastic P around the core I2 and through the sleeve II. The core I2 is rotated by the screw I6 through its threaded connection with the lubricant conduit I5, which extends through an opening I'I in the usual spider I8 positioned in the extruder bore 20. The extruder screw I6 rotates in the bore 20 on the center line of the Vsleeve II and it provides the only direct support for the core I2 in the apparatus for maintaining the core centered in sleeve II.y The opposite end of the core I2 is deectable due to the weight of the relatively long length of the core extending beyond and supported only at one end of the screw IE. Such weight is oated on the plastic P in the sleeve and the center of the core I2 is maintained on the center line of the sleeve II by the rotation of the core, which causes the plastic to rotate with it to some extent as it makes contact with the core or the member to which the core is attached, and the plastic tends to approach the speed of rotation of the core as it travels along the core.

As the plastic passes through the sleeve II, it is set therein, and emerges from the end of the sleeve as a finished tube T. The plastic P, for example may be a vulcanizable rubber compound, and it is vulcanized by means of heat supplied from the electrical resistance of the sleeve II to the current which passes between the terminals 2I and 22 which are affixed to the sleeve I I. The rubber compound is progressively vulcanized, and by the time it reaches the snubber I3, it is completely vulcanized.

It will be noted that an aceleration of the rotation of the plastic P on the core I2 takes place while the plastic is being progressively set or vulcanized. The acceleration or deceleration of the rotation of one section of the plastic with respect to the other produces a twist or spiral strains in the Walls of the tube being processed. It is desirable that the twist should occur only in the plastic before it has set to a substantial degree in order to prevent permanent strains and ssures from being produced in the tube T. This is accomplished by placing the snubber i3 on the rotating core I2 rather than on the stationary sleeve I I. It was found that such detrimental strains and fissures occured when the snubber was placed on the stationary sleeve Ii and they were eliminated or reduced. to a satisfactory degree when the snubber -l3 was placed on the rotating core t2. It is believed that the strains or ruptures in the walls of the plastic were produced. in the partially 'set plastic .by the stationary snubben because it stopped or decelerated the rotation of the section. of the plastic VVat the snubber Whereas the lcore I2 continued theretation of -other-sectionso the plastic in the sleeve it and caused a disrupting back twistto .be set up in the plastic. SuchA detrimental. effect was eliminated by the .rotating .snubbcr I3 .be-

cause the Vsection of the plastic opposite the snubber was not deceierated with respect to the other sections in the sleeve II.

As `shotvn in iigs. land 3 the expansibie snubber i3 is madeby forming a bore e3 in the outer end of the core I2.- The wall 2A of the bore is divided into 'sections 25 by slits 25,. The sections 25 are expanded by means of a 'plug 2i haviim va tapered vhead 28 and a theraded end 2s, which is screwed into a threaded counterbore Si? in the core i2. A slotted recess SI is provided in the end o the plug 2, within which a screw driver may ybe inserted to screw Ithe plug in and out of the coun-terbcre 35 to adjust the constriction between the sleeve II land the snubber I3.

The spider it is provided with the plurality of openings V3d to permit the plastic P to pass from the bore "Ztl in the head of the extruder to a tapered passage 35 in a die block 35. The plastic P is discharged from the tapered passage 35 into 45 on the-block 3S. The spider i8 and blocks 3G i' and 38 are secured in the lhead of the lcxtrucher by an assembly nut di which is screws into the bore in the head of the extruder against a flange i2 on the outer block 36, and thereby for-ces the biocks 3d and 5.8 towards the spider i8, and holds them securely place against each other.

A lubricant groove .'53 is formed Yin the face of the block 33,*and is connected by a passage d4 to 'the lubricant pipe iii or conducting the lubricant to the outer surface of the plastic in the passage''l. The lubricant passes to the inside surface of the plastic P from the vconduit I5 .into the passage 35 in the core I2. The passage d5 terminates in radial passages ld which discharge the lubricant into an annular space between the fi core I2 and the inner end of the conduit I5, through which thelubrcant passes to the inner surface of the plastic P along the lcore I2. The

lubricant is supplied to the pipe I and the con-V duit I5 under suicient pressure to cause it to i0 flow ontov'th'e surface of the plastic against Ythe extrusion pressure.

As shown in. Figs. 4, 5 and 6 the core 5i! in the sleeve 5I may be square, or of a non-circular cross-section for the purpose o making a tube having a like cross-section for its internal bore.

In that case. the snubber 52 to be placed on the end of the core should have a like cross-sectional shape as shown vin Fig. 5. A recess 53 of a noncircular cross-section is formed in the end of the core 5G. As shown in Figs. 5 and 6, the recess is of the square cross-section, and the walls thereof are divided in four sections 55 at the cornersV by slits 55. The sections 55 are expanded outwardly by a four-cornered pyramidal plug 5l, which is forced into the bore 53 by means of a screw v58 which passes through the plug 5l and is threaded into -a counterbore -5-9 in the core 5S. The tube T" manufactured by the square core 55 as shown in Figs. 4;, 5 and 6 will have asquare internal transverse cross-section.

While we have described two forms .of this invention, it will be understood that .the details may be changed Without `departing from the spirit of this invention, 4or the scope of the appended claims. y

Having .thus described our invention, wha-t we claim and desire to protect by Letters Patent is:

l. An apparatus for extruding and simultaneously setting plastic tubes vcomprising .a relatively long sleeve, a relatively long deectable core sai-d sleeve, a support at the inlet end of said sleeve only for maintaining said core centrally of said sleeve, an expansible snubber on the discharge end of said core, means for forcing plastic into said sleeve and around said core, means for lubricating the inner and outer surfaces of said plastic .in said sleeve at its inlet end, means for thermosetting said plastic during its passage through said sleeve, and means for rotating said core and said snubber in said sleeve and rotating said ,plastic by the rotation of said members.

2. An apparatus for extruding and simultaneously vulcanizing tubes of rubber compound comprising a relatively long sleeve, a relatively long deflectable core supported centrally of said sleeve at its inlet end and forming an annular passage between said sleeve and core, means for forcing vulcanizable rubber compound into said sleeveVa-nd around said core, means for lubricating the inner and outer surfaces of the rubber compound in said sleeve, means for vulcanizing said rubber compound duri-ng its passage through said sleeve, a snubber comprising an enlargement on the discharge end of said core only which reduces the cross section of said passage between said sleeve and core only at the .approximate end of said core and only at a point where the rubber compound has been vulcanized,

and means for rotating said core and said snubber which cause the rubber `compound -to rotate therewith.

WILLIAM A. M-EROK. MARK W. OLSON.

REFERENCES CKTED The following references are of record in .the

file of this patent:

UNITED STATES PATENTS Bailey June 15, 1948 

